I own a 2004 Avalanche which I really like. However, the other day, I turned on the A/C. I heard a "POP". Now the A?C only blows on the floor and on the defrost mode. It will not blow out the dash vents. Any ideas how to fix it or what the problem is? Obviously it is out of warranty. Is this a problem I can fix or do I have to take it somewhere?